The invention relates to a central heating method and plant for a building additionally provided with at least one thermodynamic device such as a heat pump or a refrigerating device.
In these machines, a cooling fluid, is, in a known manner, by passage through a pressure reducing valve, brought to a relatively low pressure which enables it to evaporate at low temperature. It is then supplied to an evaporator in which it absorbs heat until it is completely evaporated.
The cooling vapor produced in this way is then brought to a relatively high temperature by a compressor which ensures its circulation and additionally its re-heating, after which the compressed gas is supplied to a condenser in which the coolant supplies at least part of its heat to a cooling agent by condensation.
While cooling, the coolant passes from the gaseous to the liquid state before being returned to the pressure reducer in order to commence a new cycle.
It is already known to recover, for a central heating plant, the heat available in this way from the high pressure circuit of the coolant (French Patent Specification No. 2 394 026 and the German Patent Specification No. 2 515 289).
These known constructions comprise, on one hand, a water tank recovering the heat released by the condensation of the coolant and which is stored in an accumulator tank to which there are connected the return and discharge conduits of a radiator network and, on the other hand, an auxiliary boiler providing the water of the radiator network with the heat which may be lacking in the accumulator.
In the plant described in the French Patent Specification No. 2 394 026, the thermodynamic device is actuated when an aquastat detects a temperature decrease in the tank whilst the boiler is actuated by the thermostats of the radiator network and a general thermostat.
This boiler operates as follows: its return circuit takes part of the water in the conduit which, as it comes from the accumulator tank, is moving towards the radiators and after re-heating this water, its discharge circuit adds an equivalent amount of water to the conduit by means of a regulator valve.
When mixed with the water of the circuit passing through the accumulator tank, the water heated by the auxiliary boiler re-heats this water which then acts on the thermostat in order to prevent the release of heat to the condenser of the thermodynamic device.
As a result of this, during use of the auxiliary boiler, i.e. at times when heating requirements are greater, the plant is not able to recover, and therefore accumulate, heat from the thermodynamic device since it is not in operation.
It is true that even in the case in which the thermostat maintains the thermodynamic device in operation the water of the exchanger-accumulator tank, reheated by the auxiliary boiler, would then be too hot to succeed in taking heat from the condenser of the said machine since in the latter the coolant would be at a temperature almost identical to that of the water which would prevent any exchange.
This is therefore the reason why the thermodynamic machine, which is a heat pump in this case, is only actuated during the infrequent times when the water of the accumulator tank is not re-heated by the boiler which does not, however, provide sufficient use to set off the considerable investment required for a heat pump which would not have any other use so as to be able to be controlled as a function of the heating requirements alone.
On the other hand, this prevents the use of a thermodynamic machine which would have a further use such as a refrigerating device which could not be stopped and operated as a function of heating requirements but solely as a function of cooling requirements and whose heat then released to the condenser is the more considerable as without this recovery it would be lost and, in this way, may be considered to be free.
The same drawbacks are to be found in the plant disclosed in the German Patent Specification No. 2 515 289 as a result of the fact that it is designed such that the heating of the water of the accumulator tank by the heat taken from the condenser of the thermodynamic machine, which is also a heat pump not designed for other uses, is only controlled as a function of criteria which are foreign to the requirements of the thermodynamic machine itself which, whatever the case, is stopped on actuation of the auxiliary boiler which takes place at exact times.